Astronomers Describe Discovery of a Distant Cosmic Laser: “Thousands of Times More Powerful Than Our Sun”

 

Megamaser

 

Forget about the hand-held laser guns used in Star Trek. The NASA/ESA Hubble Space Telescope image above shows a megamaser, IRAS 16399-0937, located over 370 million light-years from Earth. The entire galaxy essentially acts as a cosmic laser that beams out microwave emission rather than visible light.

New Megamaser Discovery

Using the MeerKAT radio telescope, a radio telescope consisting of 64 antennas in the Northern Cape of South Africa, an international team of researchers have discovered a powerful new megamaser – a radio-wavelength laser that beams out microwave emission originating from dense gas in colliding galaxies. The galaxy merger is 6.6 billion light-years away, making this the most distant such megamaser found so far.

The team consisted of researchers from the University of the Western Cape, the University of Cape Town, Rhodes University, the South African Radio Astronomy Observatory and the South African Astronomical Observatory together with colleagues from 12 other countries.

An Exceedingly Bright Signal

When galaxies merge in collisions of cosmic proportions, the gas they contain becomes extremely dense. In particular, this can stimulate hydroxyl molecules, made of one atom of oxygen and one atom of hydrogen, to emit a specific radio signal called a maser (a maser is like a laser but emits microwave radio waves instead of visible light). When that signal is exceedingly bright, it is called a megamaser. 

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A Hydroxyl Lighthouse

“When two galaxies like the Milky Way and the Andromeda Galaxy collide, beams of light shoot out from the collision and can be seen at cosmological distances. The  hydroxyl (OH) megamasers act like bright lights that say: here is a collision of galaxies that is making new stars and feeding massive black holes,” explains Jeremy Darling, Professor of Astrophysics & CASA Director at the University of Colorado, Boulder, a megamaser expert and co-author of the study. 

The majority of megamasers are hydroxyl (OH) megamasers that emit light at a wavelength of 18cm, light that belongs to the radio part of the electromagnetic spectrum, and it is the type of light that the MeerKAT radio telescope in the Karoo is designed to capture. There are three other known megamasers for the molecules: water (H2O), formaldehyde (H2CO), and methine (CH).

 

Megamaser

 

Artist’s impression of a hydroxyl maser. Inside a galaxy merger are hydroxyl molecules, composed of one atom of hydrogen and one atom of oxygen. When one molecule absorbs a photon at 18cm wavelength, it emits two photons of the same wavelength. When molecular gas is very dense, typically when two galaxies merge, this emission gets very bright and can be detected by radio telescopes such as the MeerKAT ( © IDIA/LADUMA using data from NASA/StSci/SKAO/MolView).

LADUMA: Looking At the Distant Universe with the MeerKAT Array

One of the big MeerKAT science experiments is looking for neutral hydrogen gas in galaxies in one area of the sky, and looking for it very deeply – meaning very far from us, both in space and in time. By measuring the neutral hydrogen gas in galaxies from the distant past to now, LADUMA will contribute to our understanding of the evolution of the universe. This is no minor exercise, and so the research team comprises scientists from South Africa, Australia, Chile, France, Germany, India, Italy, Japan, the Netherlands, South Korea, Spain, the UK, and the US. “LADUMA is probing hydrogen within a single ‘cosmic vuvuzela’ that extends to when the universe was only a third of its present age,” says Associate Professor Sarah Blyth from the University of Cape Town.

“An important part of understanding how galaxies form and evolve over cosmic time is understanding the properties of their interstellar gas, from which new stars can be formed,” Rutgers University astrophysicist Andrew Baker told The Daily Galaxy. “The LADUMA team is using very sensitive MeerKAT observations of one area of the sky to study the properties of hydrogen gas in galaxies out to a distance of nine billion light years, thereby looking back in time to when the universe was only a third of its present age. As a bonus, we were also able to detect hydroxl (OH) megamasers produced in galaxy mergers out to even greater distances.”

To look for hydrogen, the team looks for light with a wavelength of 21cm that has been stretched to longer wavelengths by the expansion of the universe. However, light from other atoms and molecules is also present, and in their very first observation with MeerKAT, the team detected bright emission from hydroxyl molecules that had been even more stretched from its original wavelength of 18cm.

“It’s impressive that in a single night of observations with MeerKAT, we already found a redshift record-breaking megamaser. The full 3000+ hour LADUMA survey will be the most sensitive of its kind,” explains Dr. Marcin Glowacki, previously a researcher at the Inter-University Institute for Data-Intensive Astronomy (IDIA) and University of the Western Cape, and now based at the Curtin University node of the International Center for Radio Astronomy Research (ICRAR), who led the investigation.

When the team saw this signal in the data coming from the telescope, and confirmed that it was coming from hydroxyl, the team realized that they had a megamaser on their hands.

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“Nkalakatha”The Host Galaxy

Once the team knew it was a megamaser, they went on to look for its host galaxy. Where was the megamaser coming from? The patch of sky explored by the LADUMA team has been observed in X-rays, optical light and infra-red, so the team was able to easily identify the host galaxy. 

The host galaxy of “Nkalakatha” – Zulu word that means “big boss”– is known to have a long tail on one side, visible in radio waves. It is about 58 thousand billion billion (58 followed by 21 zeros) kilometers away, and the megamaser light was emitted about 5 billion years ago when the universe was only about two thirds of its current age. 

New Generation of Radio Telescopes Probe much Deeper into the Universe

This is the first time a megamaser has been detected at that distance from its emission at 18cm wavelength. The authors of the study point out that it is not surprising that they found such a bright megamaser, given how powerful the MeerKAT is, but the telescope is very new, so this find hopefully is one of many more to come. “MeerKAT will probably double the known number of these rare phenomena. Galaxies were thought to merge more often in the past, and the newly discovered OH megamasers will allow us to test this hypothesis,” comments Darling.

“Until very recently, radio telescopes were only able to measure the emission from neutral hydrogen gas in galaxies in the nearby Universe. But the new generation of radio telescopes like MeerKAT are much more sensitive and will let us probe much deeper into the universe than ever before,” wrote astronomer Sarah Blyth at the University of Cape Town in an email to The Daily Galaxy.

“The LADUMA survey on MeerKAT probes the emission from neutral atomic hydrogen gas in galaxies back to when the universe was only one third of its current age and will be the deepest survey of its kind until the SKA comes online,” Blyth continued in her email.  “Hydrogen gas is a major component of galaxies – it’s what stars form out of! From our survey we will be able to learn about how the gas content of galaxies has evolved over the past nine billion years of cosmic history.”

“Although LADUMA’s main aim is to search for neutral hydrogen emission, it will also detect emission from hydroxyl (OH) megamasers.” Blyth explained. One of the things we have to do for the survey is disentangle whether a signal we see is from atomic hydrogen or OH, however we expect to find far more hydrogen signals than megamasers, so most of our detections will come from atomic hydrogen gas in galaxies.”

Radio astronomy is entering a truly exciting time with the upcoming Square Kilometer Array and its pathfinder telescopes, including MeerKAT. Unplanned discoveries are starting to emerge from the unprecedented amounts of data these instruments collect. And with MeerKAT and IDIA, South Africa is right at the cutting-edge of astronomy.

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The Last Word –Jeremy Darling 

“I was thrilled when I learned about the discovery of the megamaser in the early LADUMA data because I’ve been thinking about finding distant OH megamasers and using them to study colliding galaxies for more than twenty years,” Darling wrote in an email to The Daily Galaxy. “The prediction was that they should be ‘out there’ in the early universe in large numbers, but they have been elusive for a very long time.”  

“This new discovery will be the first among many — it’s just the most obvious one at the moment.  Like stumbling across a big fossilized bone sticking out of the ground, it signifies that careful digging will uncover more.”  

“It is almost certain that if OH gigamasers billions of times stronger than the average maser in the Milky Way exist,” Darling concluded, “then MeerKAT will detect them. The big question is whether these masers have a maximum power.  Just how luminous they can be is not known.  But when two massive gas-rich galaxies collide, there is a lot of energy available to make masers.”

The NASA/ESA Hubble Space Telescope image of megamaser IRAS 16399-0937at the top of the page comprises observations captured by two of Hubble’s instruments: the Advanced Camera for Surveys (ACS), and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) gave astronomers the unique opportunity to observe the structure of IRAS 16399-0937 in detail. They found that IRAS 16399-0937 hosts a double nucleus, both buried deep within the same swirl of cosmic gas and dust and are interacting, giving the galaxy its peculiar structure. The nuclei are very different. IRAS 16399S appears to be a starburst region, where new stars are forming at an incredible rate. IRAS 16399N, however, is something known as a LINER nucleus (Low Ionization Nuclear Emission Region), which is a region whose emission mostly stems from weakly-ionized or neutral atoms of particular gasses. The northern nucleus also hosts a black hole with some 100 million times the mass of the Sun.

Maxwell Moe, astrophysicist, NASA Einstein Fellow, University of Arizona via Sarah Blyth, Andrew Baker, Jeremy Darling and SARAO

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